1. Field of the Invention
This application relates to welding power supplies and more particularly to a supply that includes a combination of a series and shunt regulating circuits that result in strict regulation of the weld capacitor output voltage.
2. Description of the Prior Art
Welding power supplies are known in the prior art. One type of supply is described in U.S. Pat. No. 3,604,888. Operation of the described supply relies on a charge controller which gates a silicon controlled rectifier (SCR) that is connected in series with a full wave rectifier and a welding energy storage capacitor. Controllers of this design have an inherent problem in that they frequently charge the storage capacitor to a level beyond that desired. This consequence results from the fact that SCR's or triacs cannot be turned off coincident with the voltage of the storage capacitor reaching its pre-selected value. The series SCR continues to conduct and charge the weld capacitor until the rectifier line current goes to zero, causing a capacitor overcharge condition.
Another such supply is described in U.S. Pat. No. 3,436,514. Operation of the described power supply here again relies upon supply of energy from a full wave bridge rectifier to a storage capacitor through a charging circuit using a first series SCR. A second SCR in series with the storage capacitor's discharge path is gated by a timing pulse network such that the timing pulses prevent simultaneous conduction of both charging and discharging SCR's. However, the supply fails to provide storage capacitor voltage regulation or protection against overcharge occurring prior to the charging SCR turn off. In addition, neither the supply described in U.S. Pat. No. 3,604,888 nor the one described in U.S. Pat. No. 3,436,514, provide compensation for any charge leakage from the storage capacitors.